With no guidance or clarity from the Trump administration, state officials are agonizing over what to do. Many expressed a sense of urgency, saying they needed to make decisions soon on rates to be charged in 2018.

Trump administration officials were invited to speak to state insurance regulators and were listed in the program for at least one public session, but they did not show up at that event to provide the promised update on federal policy.

“Most of us are hoping and praying that this gets resolved,” said David Shea, a health actuary at the Virginia Bureau of Insurance. “But that’s not the case right now.”

Without the federal subsidies, insurers would need to get the money — estimated at $7 billion to $10 billion next year — from another source. And that means higher premiums, state officials said.

The officials here are wrestling with several questions: How much should premiums be increased? Who should pay the higher premiums? Is there any way to minimize the effect on low-income people? Is it better to assume that the cost-sharing subsidy payments will or will not be made in 2018? What happens if state officials guess wrong?

State officials said they would allow insurers to impose a surcharge on premiums if the federal government cuts off funds for the cost-sharing subsidies.

Paul Lombardo, a health actuary at the Connecticut Insurance Department, said officials there might direct insurers to spread the cost across all of their health plans, both on and off the insurance exchange created under the Affordable Care Act.

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Alfred W. Redmer Jr. at the meeting on Monday in Philadelphia.Credit
Mark Makela for The New York Times

By contrast, Florida has asked insurers to load all of the extra cost into the prices charged for midlevel “silver plans” sold on the exchange. The federal government would then absorb almost all of the cost through another subsidy program, which provides tax credits to help low-income people pay premiums, Mr. Wright said. The tax credits generally increase when premiums rise.

J. P. Wieske, the deputy insurance commissioner in Wisconsin, said that two companies, Anthem and Molina Healthcare, were leaving the state’s marketplace in 2018 and that two others, Humana and UnitedHealth, exited in previous years. As a result, he said, more people will be enrolled in smaller local health plans that could be more affected by a termination of federal subsidy payments.

“Carriers left in the Wisconsin market are smaller, local plans,” Mr. Wieske said. “Particular carriers could have huge surges in population, going from 7 or 8 percent of their business in the individual market to 30 or 40 percent. If that’s the case, if it’s 30 or 40 percent of their business in the individual market, that’s obviously a gargantuan risk.”

The risks for consumers are also high, Mr. Wieske said. “Consumers,” he said, “could be stuck in a zombie plan, an insurer that is essentially no longer able to do business in the worst-case scenario, or consumers may have to move to another insurer with different health care providers.”

Officials in many states must decide this month on insurance rates for next year.

“We are holding off making those decisions until the very last possible minute,” said Julie Mix McPeak, the Tennessee insurance commissioner. “In doing so, we are really making it difficult for consumers who need information about open enrollment — who’s participating in the market and what the rates might be. We don’t know the answers to any of those questions.”

The uncertainty stems not only from the White House and Congress, but also from federal courts.

House Republicans challenged the cost-sharing payments in a lawsuit in 2014. A federal judge ruled last year that the Obama administration had been illegally making the payments, in the absence of a law explicitly providing money for the purpose. The case is pending before the United States Court of Appeals for the District of Columbia Circuit, which has held it “in abeyance” at the request of House Republicans and the Trump administration.

The administration has been providing funds for cost-sharing subsidies month to month, with no commitment to pay for the remainder of this year, much less for 2018.

“I am very fearful that we’ll have insurers make a decision to leave markets as a result of the uncertainty,” said Ms. McPeak, who is the president-elect of the National Association of Insurance Commissioners. “It’s somewhat inequitable to ask insurers to sign a contract that binds them but may not bind the federal government.”

The Affordable Care Act requires an annual review of health insurance rate increases, and states are taking different approaches.

Nebraska initially told insurers to file 2018 rates on the assumption that the cost-sharing subsidies would continue. But “because of the confusion in Washington,” said Martin W. Swanson of the Nebraska Insurance Department, the state later told insurers to assume that they would not receive the subsidy payments.

Mike Chaney, the Mississippi insurance commissioner, and Allen W. Kerr, the Arkansas insurance commissioner, said they had instructed companies to assume that they would receive the cost-sharing subsidies next year. Michigan has told insurers to submit two sets of rates, one with the subsidies and one without.

Michael F. Consedine, the chief executive of the National Association of Insurance Commissioners, said that without a firm commitment of federal funds for the cost-sharing subsidies, “we have grave concerns about the long-term viability of the individual health insurance market in a number of states.”

“We need some step right away,” Mr. Consedine said, “either by action of Congress or by direction of the administration, to ensure that Americans continue to have access to coverage.”